"We always expected a tough challenge in the House of Lords, and Lord Dear's 'fatal motion' - very rarely used - demonstrates the lengths to which a minority of peers are, sadly, still prepared to go to deny full equality to lesbian, gay and bisexual people.

"In the last 24 hours alone, opponents of equality in the House of Lords have compared loving, committed relationships to incest and polygamy.

"Britain's 3.7 million gay people don't deserve to be second class citizens in their own country. A tough fight lies ahead and we'll continue to work tirelessly every single day to get equal marriage through the Lords."

But Colin Hart, campaign director for the Coalition for Marriage, said: "The Government may have won the vote today, but what was clear from the debate was the huge opposition to almost every part of the Bill.

"We will continue to campaign to save traditional marriage and today's vote and the concerns expressed by many peers mean we will be able to introduce safeguards that will protect teachers, registrars, chaplains and anyone who works in the public sector. And if the Government refuse to accept these changes, they risk losing the legislation at third reading."